1. Field of the Invention
The present invention relates to a nitride semiconductor light emitting device and more particularly, to a nitride semiconductor light emitting device adapted for use at low voltage.
2. Background Art
Nitride semiconductors have been put into practice in a variety of products as a material for light emitting devices and electronic devices. Nitride semiconductor devices disclosed in JP-A-2000-307149 are provided with a high-concentration doped layer and a low-concentration doped layer intermediate between a p-type contact layer and a p-type clad layer. The nitride semiconductor device is so arranged as having such a structure as mentioned above, so that impurity concentrations of the p-type layers are optimized, thereby reducing a working voltage.    [Patent Literature 1] JP-A-2000-307149    [Patent Literature 2] JP-A-2000-164922
For a factor determining a working voltage of a nitride semiconductor device, mention is made of the discontinuous quantity of a band gap at the heterojunction. If the discontinuous quantity of a band gap at the heterojunction at which carriers are to be transported is great, it serves as a barrier in the course of transport of carriers, thus being unfavorable from the standpoint of low working voltage. However, in such conventional nitride semiconductor light emitting device as set out above, no design consideration is given to the band discontinuous quantity, leading to a problem in that a difficulty is involved in realizing a low working voltage while keeping emission output power.